For a semiconductor element, a technique has been known to establish electrical coupling between electrodes provided on different layers over a circuit board. According to the technique as described in Japanese Unexamined Patent Publication No. 10-96960 for example, contact holes are formed by using photolithography and etching, and then an electrically conductive material is buried in the contact holes for providing electrical coupling between the electrodes.
However, using photolithography and etching involves pattern-forming, which complicates the manufacturing steps and requires vacuum equipment and many chemicals, resulting in higher manufacturing costs.
Meanwhile, a technique for easily forming contact holes has been known for example, as disclosed in Japanese Unexamined Patent Publication No. 2-21507. According to the technique, in forming contact holes for both sides of a base member composing a conductive sheet, through holes are mechanically formed in the base member by using a needle or the like instead of photolithography and etching.
Based on this technique, the following method may be used for a circuit board that includes a first electrode provided on a substrate, an interlayer film covering the first electrode and a second electrode provided on the interlayer film: the interlayer film is mechanically perforated or everted by using a needle or the like to easily form contact holes between the first and second electrodes; and a conductive material is buried in the contact holes for providing electrical coupling between the first and second electrodes.
In the case of perforating the interlayer film that covers the first electrode using a needle or the like to form contact holes, however, if the diameter of the needle is small, the diameter of the contact holes formed in the interlayer film is also correspondingly small. In this case, the contact holes are blocked due to the elastic force of the interlayer film. Therefore, in burying a conductive material in the contact holes, the conductive material can not reach the surface of the first electrode since the contact holes are blocked halfway.
As a result, electrical coupling between the first and second electrodes is precluded. Also, in the case of everting the interlayer film on the electrode by using a needle to form contact holes, and burying a conductive material therein, the everted portions of the interlayer film form projections on the interlayer film. If wires coupled to the contacts are formed on the interlayer film in this state, wire-breaking is likely to occur on the projections.